Systemd 246 has been released. There is an incredibly long list of new
features, many of which have to do with support for encrypted and signed
disk volumes. “Various command line parameters and configuration file settings that
configure key or certificate files now optionally take paths to
AF_UNIX sockets in the file system. If configured that way a stream
connection is made to the socket and the required data read from
it. This is a simple and natural extension to the existing regular
file logic, and permits other software to provide keys or
certificates via simple IPC services, for example when unencrypted
storage on disk is not desired.“

Source: LWN.net – systemd 246 released